The chemical name of Sitagliptin is (3R)-3-amino-1-[3-(trifluoromethyl)-5,6,7,8-tetrahydro-1,2,4-triazolo[4,3-a]pyrazin-7-yl]-4-(2,4,5-trifluorophenyl)butan-1-one, whose structure is of formula 1:

Sitagliptin is a dipeptidyl peptidase-IV (DPP-IV) inhibitor, and used to treat type II diabetes in clinic.
At present, the methods for preparing Sitagliptin are as follows:
Route I (Reference Document 1): (2R)-4-Oxo-4-[3-(Trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine: A Potent, Orally Active Dipeptidyl Peptidase IV Inhibitor for the Treatment of Type 2 Diabetes, Journal of Medicinal Chemistry (J. Med. Chem.), 2005, V11, 48, 141-151, Kim D, et al):
wherein -Boc group is tert-butoxycarbonyl. HOBT is 1-hydroxybenzotriazole, EDC is 1,2-dichloroethane, DIPEA is N,N-diisopropyl ethylamine (these groups or abbreviations thereof have the same definitions at each occurrence in structure formula and the description hereinafter).
Route II (Reference Document 2): WO 2004087650, publication date: Oct. 14, 2004, Applicant: Merck & Co. INC.):
wherein —OBn group is benzyloxy. NMM is N-methyl morpholine, ACN is aminochloronaphthoquinone (these groups or abbreviations thereof have the same definitions at each occurrence in structure formula and the description hereinafter).
It can be seen that compound 2 ((R)-3-(tert-butoxycarbonylamino)-4-(2,4,5-trifluorophenyl)butyric acid) and compound 3 ((R)-3-(benzyloxyamino)-4-(2,4,5-trifluorophenyl)butyric acid) are important intermediates for preparation of sitagliptin.
Wherein, the synthetic route of the intermediate compound 2 is shown as below (see reference document 1):

The synthetic route of the intermediate compound 3 is shown as below (see reference document 2):
wherein DMAP is 4-dimethylaminopyridine, (S)-Binap-RuCl2 is (S)-binaphthyl diphenylphosphine-ruthenium chloride, DIAD is triphenylphosphine and diisopropyl azodicarboxylate, PPh3 triphenylphosphine.
From the synthetic diagram of the intermediate 1 and intermediate 2, it can be seen that compound 1 and 2 are both prepared using trifluoro benzyl derivatives as the starting materials, and their common problems include: very complicated reactions with too long reaction route; difficult to control the quality and yield of the products; much materials consumed; expensive starting materials; high cost; and harsh operating conditions.